超时，思路感觉很好，每次反转，

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        int index=1;
        ListNode* tem=head;
        while(tem)
        {
            if(index++ %2 == 1)
            {
                tem->next=reverseList(tem->next);
            }
            else
                tem=tem->next;
        }
    }
    ListNode* reverseList(ListNode* head) {
		if (head == NULL)
			return head;
		ListNode* H = head;
		head = head->next;
		H->next = NULL;
		while (head)
		{
			ListNode* next = head->next;
			head->next = H;
			H = head;
			head = next;
		}
		return H;
	}
};

　　还有一个思路是：从中间断开，找到后一半的链表，反转后一半链表，依次插入

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        if(head == NULL || head->next==NULL || head->next->next==NULL)
            return ;
        ListNode* slow=head,*fast=head;
        while(fast)
        {
            slow=slow->next;
            
            fast=fast->next->next;
            if(fast->next==NULL || fast->next->next==NULL)
                break;
        }
        ListNode* second=(slow->next);
        slow->next=NULL;
        second=reverseList(second);
        ListNode* tem=head;
        while(second)
        {
            ListNode* sec_t=second->next;
            second->next=tem->next;;
            tem->next=second;
            tem=tem->next->next;
            second=sec_t;
        }
        
	}
	ListNode* reverseList(ListNode* head) {
		if (head == NULL)
			return head;
		ListNode* H = head;
		head = head->next;
		H->next = NULL;
		while (head)
		{
			ListNode* next = head->next;
			head->next = H;
			H = head;
			head = next;
		}
		return H;
	}
};